Needle comb reticle pattern for critical dimension and registration measurements using a registration tool and methods for using same

ABSTRACT

Needle comb reticle patterns for use in both critical dimension analysis and registration analysis with a registration tool is disclosed. One embodiment of a needle comb reticle pattern includes a box-in-box feature flanked on two adjacent sides by needle combs with tapered flat-tipped needles. Another embodiment of a needle comb reticle pattern includes a box-in-box feature flanked on two adjacent sides by needle combs with tapered flat-tipped needles and flanked on the other two adjacent sides by reference bars. Yet another embodiment of a needle comb reticle pattern includes two complementary needle comb reticle sub-patterns each sub-pattern including a box-in-box feature with four flanking needle combs. A registration tool can be used with the needle combs and reference bars to measure critical dimension of a semiconductor process. The registration tool can also be used with the box-in-box feature to measure registration between two adjacent layers during semiconductor fabrication. Reticles, fields within reticles, masks and wafers including the needle comb reticle pattern of the present invention are also disclosed. Additionally, methods for analyzing critical dimension and registration and characterizing needle comb reticle measurements to critical dimension using the needle comb reticle patterns of the present invention are also disclosed.

FIELD OF THE INVENTION

[0001] The present invention relates generally to metrology of semiconductor manufacturing processes. More particularly, the present invention is a needle comb reticle pattern for simultaneously making critical dimension (CD) measurements of device features and registration measurements of mask overlays relative to semiconductor wafers during processing of semiconductor wafers.

BACKGROUND OF THE INVENTION

[0002] Lithographic and etch processes used in semiconductor device manufacturing are subject to variations in exposure, focus and alignment. Generally, less variation in such semiconductor manufacturing processes leads to higher yields. Because of such process variations, patterns developed by lithographic processes must be continually monitored, or measured, to determine if the dimensions of the patterns are within acceptable ranges and to determine whether the multiple mask layers, or overlays, are properly aligned and not biased or skewed.

[0003] Conventionally, monitoring of pattern features and measurement of critical dimension (CD) may be performed using a scanning electron microscope (SEM) tool and/or an automatic force microscopy (AFM) tool. Pattern placement is measured with an and optical registration tool. While SEM metrology provides very high resolution, it is expensive to implement, relatively slow in operation.

[0004] AFM also provides high resolution but is typically even slower than SEM. The terms “optical metrology system”, “overlay metrology system” and “registration tool” are used interchangeably herein. Optical metrology systems overcome many of the problems associated with SEM and AFM metrology but are unable to resolve adequately for feature dimensions of less than about 1 μm. SEM measurements can take 8-15 seconds per measurement depending on the complexity of the task being measured, e.g., number of scans per wafer, location of measurement points, etc. AFM measurements are measured in minutes per measurement (not seconds) because of long setup times and slow scan times. A registration tool can make measurements approximately every 0.5 to 2 seconds, or at a rate of approximately 1800 to 7200 measurements per hour. Thus, registration tools are clearly faster than SEM or AFM, and hence, more suited to in-line process measurement.

[0005] State-of-the-art semiconductor devices have submicron features. Accordingly, there is a need in the art for systems and methods for monitoring pattern features with dimensions on the submicron level that is inexpensive, capable of high speed operation and subject to automation.

[0006] U.S. Pat. No. 5,701,013 to Hsia et al. discloses a wafer metrology pattern integrating both overlay and critical dimension features for SEM and AMF measurements. The Hsia et al. pattern, or test mask target, contains lines measuring 0.25 μm, 0.3 μm and 0.5 μm in width as well as a centrally positioned box for reference. The Hsia et al. pattern is intended to be measured with a metrology tool utilizing AFM.

[0007] U.S. Pat. Nos. 5,712,707 and 5,757,507, both to Ausschnitt et al., disclose a wafer target for determining bias or overlay error in a substrate formed by a lithographic process and methods for using same. The '707 and '507 Ausschnitt et al. target includes a pair of straight vernier arrays of parallel elements, a staggered vernier array of parallel elements, and, optionally, at least one image shortening array on the substrate. The '707 and '507 Ausschnitt et al. target allows measurement of bias and overlay error in deposited lithographic etch patterns that are human readable during substrate processing.

[0008] U.S. Pat. No. 5,805,290 to Ausschnitt et al. discloses a level specific target array and method of optical metrology of unresolved pattern arrays. The '290 Ausschnitt et al. level specific target array includes a first target portion with four outer arrays of parallel lines oriented coincident with the sides of a box, and a second target portion with four inner arrays of discrete, square elements oriented within and concentric to the outer arrays. First and second target portions are printed on different levels during semiconductor fabrication and allow for measurement for bias and overlay error with conventional optical metrology tools and without use of SEM or AFM tools, except for calibration.

[0009] U.S. Pat. Nos. 5,953,128 and 5,976,740, both to Ausschnitt et al., disclose optically measurable serpentine edged, reverse tone targets used in controlling focus and exposure parameters of lithographic processes and methods for using same. The '128 and '740 Ausschnitt et al. targets also disclose needle comb elements with symmetrical stepped tapering and single-sided stepped tapering. The invention provides complementary tone patterns of shapes and spaces on a resist film on a substrate. Bias and overlay errors are then measured as functions of deviations from the expected lithographic etching norms provided by the reverse patterns.

[0010] U.S. Pat. No. 6,023,338 to Bareket discloses a target, associated apparatus and methods for determining offset between adjacent layers of a semiconductor device. The Bareket target is composed of alternating periodic structures on two successive layers of a semiconductor wafer. As electron beams are scanned across the periodic gratings of the Bareket target, relative phase shift between the two layers, and hence alignment, may be determined.

[0011] Ausschnitt et al., Seeing the forest for the trees: a new approach to CD control, SPIE Vol. 3332, 1998, pp. 212-20, discloses optical critical dimension measurement of pattern arrays (also known as Schnitzl arrays) whose individual features need not be resolved by the metrology tool. However, Schnitzl arrays alone do not provide for registration measurements to detect bias and overlay error.

[0012] Kim et al., Automatic In-situ Focus Monitor Using Line Shortening Effect, SPIE Conference on Metrology, Inspection, and Process Control for Microlithography XIII, Santa Clara, Calif., March 1999, pp. 184-93, discloses a box-in-box pattern with conventional line and space patterns along edges of the inner and outer boxes. Kim et al. considered dagger (or wedge) tapered needle points to be the most sensitive to the line shortening effect. However, Kim et al. concluded that dagger needle points are impractical because of limitations in the angles allowed with most electron-beam mask generation systems, e.g., 0°, 45° and 90°. Kim et al. also contemplated the use of stair-stepped needle patterns but rejected them because of the prohibitively large electron-beam mask data size and difficulty in checking and verifying defect free masks with complex stair-stepped needle patterns.

[0013] While these prior art approaches have addressed many problems faced by semiconductor process control engineers, there still exists a need in the art for a target or pattern that simultaneously provides for critical dimension analysis and registration measurements, that is cost effective, capable of high-speed operation, subject to in-line process automation and that can be placed in scribe lines at arbitrary locations on a semiconductor wafer.

SUMMARY OF THE INVENTION

[0014] The present invention comprises needle comb reticle patterns that allow registration measurements and CD measurements using a single registration tool at a single location on a semiconductor wafer. The needle comb reticle patterns of the present invention save time and cost by eliminating the need to make registration and CD measurements separately with different tools.

[0015] An embodiment of a needle comb reticle pattern of the present invention includes a box-in-box registration feature, surrounded on two adjacent sides by needle comb features. Another embodiment of a needle comb reticle pattern of the present invention includes a box-in-box registration feature, surrounded on two adjacent sides by needle comb features and reference bars adjacent to the other two sides of the box-in-box feature. Yet another embodiment of a needle comb reticle pattern of the present invention includes a box-in-box registration feature surrounded on all sides by needle comb features. A preferred embodiment of a needle comb reticle pattern of the present invention includes two complementary needle comb reticle sub-patterns. Needle comb features on opposite sided of the box-in-box registration feature have needles pointing in the same direction.

[0016] The box-in-box feature includes an inner box and an outer box which are mutually concentric. Each needle comb feature includes a base from which stair-stepped, tapered needles extend and point toward the outer box of the box-in-box feature. These stair-stepped needles have a variable width, much smaller than length, i.e., variable width<<length. The variable width of each stair-stepped needle runs from larger-than-stepper resolution to sub-resolution width. When viewed with an optical tool, the comb feature will appear as an opaque bar of width that depends on the degree to which the stepper system is in focus. The more out of focus, the narrower the width of the comb feature. The individual needles cannot ordinarily be resolved without the aid of high magnification, such as may be provided with a SEM tool.

[0017] The needle comb reticle pattern of the present invention allows use of a single registration tool to measure both wafer alignment and resolution, as characterized to critical dimension (CD), saving time ordinarily devoted to separate measurements. Furthermore, the needle comb reticle pattern may be placed anywhere on a semiconductor wafer in the scribe lines, thus, conserving wafer real estate for production devices.

[0018] During the wafer alignment process, a needle comb reticle pattern is viewed with an optical measuring device, such as a registration tool. Suitable registration tools, also known as overlay metrology systems, include e.g., model numbers 5200XP and 5300, from KLA-Tencor, San Jose, Calif. When viewed by the registration tool, the sub-resolution portion of the needles within the needle comb features will appear shortened. The extent of shortening depends on the lens of the stepper tool, its optical set-up and process capability. The registration tool can then measure the apparent shift in the needle comb marks relative to the center of the overlay printed at the same level. This allows for an amplified measurement relation to the exposure system's resolution capability. Furthermore, CD and focus measurements may be taken while simultaneously measuring for registration. Using a registration tool in this way is generally faster than previous registration tools used in conjunction with SEM or AFM tools.

[0019] Reticles, fields of reticles, masks and wafers including the needle comb reticle pattern of the present invention are encompassed by the present invention. Additionally, methods of analyzing critical dimension and registration of microelectronic lithographic processes and for characterizing measurements form a needle comb reticle pattern to pattern critical dimension are also encompassed by the present invention.

[0020] These embodiments, methods and attendant advantages of the present invention will be readily understood by reading the following detailed description in conjunction with the accompanying figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the drawings, which illustrate what is currently regarded as the best mode for carrying out the invention and in which like reference numerals refer to like parts in different views or embodiments:

[0022]FIG. 1 is an embodiment of a needle comb reticle pattern of the present invention, including both box-in-box and needle comb features in a single pattern.

[0023]FIG. 2 is a higher magnification diagram of two comb needles from the embodiment of FIG. 1.

[0024]FIG. 3 is a plan view of an exemplary semiconductor wafer containing a needle comb reticle pattern in accordance with the present invention.

[0025]FIG. 4 is a schematic diagram illustrating the exposure process using the needle comb reticle pattern of the present invention.

[0026]FIG. 5 is a schematic diagram of a registration tool for measuring CD and registration in accordance with the present invention.

[0027]FIG. 6 is a flow chart of a method of analyzing critical dimension and registration using a single registration tool and a needle comb reticle pattern of the present invention.

[0028]FIG. 7 is an alternative embodiment of a needle comb reticle pattern of the present invention, including both box-in-box and needle comb features in a single pattern.

[0029]FIG. 8 is a plan view of an exemplary semiconductor wafer illustrating a field of a reticle containing at least one active device pattern and at least one needle comb reticle pattern of the present invention.

[0030]FIG. 9 is a flow chart of a method of characterizing measurements from a needle comb reticle pattern to pattern critical dimension in accordance with the present invention.

[0031]FIG. 10 is a presently preferred embodiment of a needle comb reticle pattern of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0032] U.S. Pat. No. 5,701,013 to Hsia et al. and U.S. Pat. No. 6,023,338 to Bareket are expressly incorporated herein by reference for all purposes. U.S. Pat. Nos. 5,712,707, 5,757,507, 5,805,290, 5,953,128, 5,976,740 all to Ausschnitt et al. are expressly incorporated herein by reference for all purposes. The following technical articles are also expressly incorporated herein by reference for all purposes: Ausschnitt et al., Seeing the forest for the trees: a new approach to CD control, SPIE Vol. 3332, 1998, pp. 212-20, and Kim et al., Automatic In-situ Focus Monitor Using Line Shortening Effect, SPIE Conference on Metrology, Inspection, and Process Control for Microlithography XIII, Santa Clara, Calif., March 1999, pp. 184-93.

[0033] As shown in FIG. 1, an embodiment of the needle comb reticle pattern 100 of the present invention includes a box-in-box feature 102 including an inner box 104 and an outer box frame 106. Flanking the box-in-box feature 102 are needle comb top 108 and needle comb left 110. Also flanking the box-in-box feature 102 are reference bar right 112 and reference bar bottom 114. An optional outline mark 122 is also shown in FIG. 1. Reference bar right 112 functions as a solid reference mark for needle comb left 110. Reference bar bottom 114 functions as a solid reference mark for needle comb top 108. Both reference bars right 112 and bottom 114 maintain their same positions relative to the process condition. Needle comb top 108 and needle comb left 110 each include a plurality of needles 116 emanating from a solid bar base 122 and pointing inward toward the box-in-box feature 102.

[0034] The terms “needle comb reticle pattern” and “needle mark” may be used interchangeably herein. It should be understood by one of ordinary skill in the art that a needle comb reticle pattern 100, as described herein and as applied to a given reticle or mask, will alternate between merely the inner box 104 of the box-in-box feature 102 on a given layer, n, and the remaining features, i.e., the outer box frame 106 in combination with the needle combs 108, 110 and reference bars 112, 114, without inner box 104 placed on the next layer, n+1. The inner box 104 may also be referred to as a “target mark” or “target” and these terms will be used synonymously herein. The outer box frame 106 may also be referred to as an “overlay” or “overlay mark” and these terms will be used synonymously herein.

[0035] The inner box 104 of the box-in-box feature 102 is a target mark. In the preferred embodiment of the invention, inner box 104 is placed on a previous layer during semiconductor fabrication and the outer box frame 106 on the current layer is referenced to the inner box 104. The needle comb mark is printed on the same layer as the overlay mark. Perfect registration between previous and current layers will be indicated using a registration tool (not shown) where the inner box 104 appears centered inside the outer box frame 106.

[0036] For a 0.25 μm feature size semiconductor fabrication process, the length, l_(n), of needles 116 is approximately 1.5 82 m. The pitch, p, or separation of the needles 116, is approximately 0.25 μm. The points of needles 116 are spaced approximately 0.5 μm from the outer edge 118 of outer box frame 106 and a distance, l_(o), of approximately 18 μm from proximate edges 120 of the reference bars 112, 114. The measured length, l_(m), (using a registration tool) will tend to be longer than the distance, l_(o), in accordance with the line shortening effect of the needles 116 when out of focus. The inner box 104 measures approximately 7 μm on a side and has an area of approximately 49 μm². In perfect registration, an approximately 3 μm space, s, separates inner box 104 from outer box frame 106. The degree to which to adjacent process layers are out of registration may be measured by the difference between the measured separation and the nominal value of s=3 μm. Outer box frame 106 has a width, w_(o), of approximately 2 μm, as shown in FIG. 1. Right reference bar 112 and bottom reference bar 114 are both of width, w_(r), of approximately 2 μm, as shown in FIG. 1. The entire needle comb reticle pattern 100 is substantially square in shape and measures approximately 25 μm on a side, covering an area of approximately 620 μm². However, other embodiments of a needle comb reticle pattern in accordance with the present invention may be formed of substantially octagonal or circular patterns to maximize sensitivity to lens aberrations.

[0037] A scribe line on a semiconductor wafer is approximately 50 μm to 60 μm in width and provides a boundary and point of separation between each integrated circuit die being fabricated on the semiconductor wafer. The needle comb reticle pattern 100 of the present invention is small enough to be placed on any scribe line at any location along the grid formed by the scribe lines on the wafer. Preferably, the needle comb reticle pattern 100 is placed on a scribe line and adjacent to an active component region or device pattern that forms an integrated circuit die. Once wafer processing in complete, the individual dice are singulated from the wafer by scribing the scribe lines with a diamond or other suitable scribing tool and breaking the wafer along the scribe lines or sawing through the wafer along the scribe lines. The needle comb reticle patterns 100 serve no purpose once the individual dice are singulated, so their destruction during scribing or sawing is of no consequence.

[0038]FIG. 2 is a high magnification view of a portion of a needle comb 108, 110 illustrating only two of the plurality of needles 116. Needles 116 may taper in width by stair-steps 116 s which, as shown, may be relatively shallow. Needles 116 are widest at the solid bar base 122 of the needle combs 108, 110 and taper gradually to a flat tip 224. Flat tips 224 are preferred over acute needle points because the shallow angle formed from tip to base, for the same length, gives a greater change in needle length for the same change in resolution. While the actual taper of the needles 116 in the needle comb reticle pattern is a stair-step function, the lithographic process (electron-beam) used to fabricate the mask will smooth the transitions in the stair-steps actually produced in the mask. As noted previously, the width of each stair-stepped needle 116 varies from larger than stepper resolution to smaller than stepper resolution.

[0039]FIG. 3 illustrates a plan view of an exemplary semiconductor wafer 300 including one or more needle comb reticle patterns 100, 700, 1000 in accordance with the invention. The semiconductor wafer 300 includes active device patterns 304 separated by scribe lines 302. Note that the scribe lines 302 are not drawn to scale in FIG. 3, but are oversized for clarity to better illustrate the placement of needle comb reticle patterns 100, 700, 1000 on scribe lines 302. The semiconductor wafer 300 also includes needle comb reticle patterns 100, 700, 1000 either adjacent to active device patterns 304 in scribe lines 302 or in regions where an active device pattern 304 will not fit, i.e., along the perimeter of the semiconductor wafer 300. FIG. 3 may also be representative of a plan view of a mask for use in conventional optical lithography, wherein the entire surface of a semiconductor wafer is optically exposed in a single step.

[0040] Referring to FIG. 4, a schematic diagram illustrating an exposure process using the needle comb reticle pattern 100, 700, 1000 of the present invention is shown. During semiconductor fabrication, the needle comb reticle pattern 100, 700, 1000 is first placed on a mask or a reticle 400. The needle comb reticle pattern 100, 700, 1000 along with an active device pattern 404 is then projected onto the surface of semiconductor wafer 300 resting on a registration tool stage 410 using an exposure tool 402 during optical lithography. The exposure tool 402 includes a lens 406 used to project the image from the reticle 400 onto the surface of the semiconductor wafer 300. This process may be repeated for each device pattern 404 projected onto the surface of the semiconductor wafer 300 to form an integrated circuit die 408. The process of stepping each reticle pattern is well known to one of ordinary skill in the art and, thus, will not be further detailed herein.

[0041] Referring to FIG. 5, a schematic diagram of a registration tool 500 for measuring CD and registration in accordance with the invention is shown. FIG. 5 shows a registration tool 500 electrically coupled with cabling 508 to a monitor for viewing a magnified needle comb reticle pattern 510 on the surface of a semiconductor wafer 300. FIG. 5 also shows a semiconductor wafer 300 on a registration tool stage 502 with at least one needle comb reticle pattern 100, 700, 1000 adjacent to an active device pattern 504, both on the surface of the semiconductor wafer. The registration tool 500 as configured in FIG. 5, may be used to simultaneously measure CD and registration.

[0042]FIG. 6 is a flow chart of a method 600 of analyzing CD and registration using a single registration tool and the needle comb reticle pattern of the present invention. The method includes providing a semiconductor wafer with at least one needle comb reticle pattern 602 such as that shown in FIG. 1. A registration tool 604 is provided, the tool including a registration tool stage, an optical registration tool and a monitor electrically coupled to the optical registration tool. The semiconductor wafer is placed on the registration tool stage 606. The optical registration tool is aligned with the at least one needle comb reticle pattern 608 and CD and registration are analyzed from lengths measured from the at least one needle comb reticle pattern 610. The aligning step 608 and the analyzing step 610 may be repeated, in turn, for each needle comb reticle pattern on the semiconductor wafer. Suitable registration tools for use with the needle comb reticle pattern and method of the present invention, include e.g., model numbers 5200XP and 5300, from KLA-Tencor, San Jose, Calif. Other similar overlay metrology systems are also suitable.

[0043]FIG. 7 is an alternative embodiment of a needle comb reticle pattern 700 of the present invention, including both box-in-box and needle comb features in a single pattern. The alternative embodiment of the needle comb reticle pattern 700 of the present invention includes a box-in-box feature 102 including an inner box 104 and an outer box frame 106. Flanking the box-in-box feature 102 are needle comb top 108 and needle comb left 110. Inner right edge 720 of outer box frame 106 functions as a solid reference mark for needle comb left 110. Inner bottom edge 722 of outer box frame 106 functions as a solid reference mark for needle comb top 108. Inner edges 720 and 722 are formed on the same layer as needle comb top 108 and needle comb left 110. Inner edges 720 and 722 also maintain their same positions relative to the process condition. Needle comb top 108 and needle comb left 110 each include a plurality of needles 116 emanating from a solid bar base 122 and pointing inward toward the box-in-box feature 102 like those described for the embodiment of FIG. 1.

[0044] For a 0.25 μm feature size semiconductor fabrication process, the length, l_(n), of needles 116 is approximately 1.5 μm. The pitch, p, or separation of the needles 116, is approximately 0.25 μm. The points of needles 116 are spaced approximately 0.5 μm from the outer edge 118 of outer box frame 106 and a distance, m_(o), of approximately 15.5 μm from inner edges 720, 722 of outer box frame 106. The measured length, m_(m), (using a registration tool) will tend to be longer than the distance, m_(o), in accordance with the line shortening effect of the needles 116 when out of focus. The inner box 104 measures approximately 7 μm on a side and has an area of approximately 49 μm². In perfect registration, an approximately 3 μm space, s, separates inner box 104 from outer box frame 106. The degree to which to adjacent process layers are out of registration may be measured by the difference between the measured separation and the nominal value of s=3 μm. Outer box frame 106 has a width, w_(o), of approximately 2 μm, as shown in FIG. 1. The entire needle comb reticle pattern 700 is substantially square in shape and measures approximately 22 μm on a side, covering an area of approximately 480 μm².

[0045]FIG. 10 is a presently preferred embodiment of a needle comb reticle pattern 1000 of the present invention. Needle comb reticle pattern 1000 includes two complementary but identically dimensioned needle comb reticle sub-patterns 1000A, 1000B. Needle comb reticle sub-pattern 1000A includes a box-in-box feature 102 including an inner box 104 and an outer box frame 106. Flanking the box-in-box feature 102 are needle comb top 1002, needle comb right 1004, needle comb bottom 1006 and needle comb left 1008. Note that both needle comb top 1002 and needle comb bottom 1006 have needles pointing in the same direction vertically (upward shown but downward will also work) which essentially doubles the focus measurement sensitivity vertically. Likewise note that both needle comb left 1008 and needle comb right 1004 have needles pointing in the same direction horizontally (pointing to the left shown, however, pointing to the right will also work) which essentially doubles the focus measurement sensitivity horizontally. Needle comb reticle sub-pattern 1000B is adjacent needle sub-pattern 1000A and shown below. However, needle comb reticle sub-pattern 1000B may abut sub-pattern 1000A on any side, consistent with the present invention.

[0046] On a given layer n of an integrated circuit during processing, needle combs 1002, 1004, 1006 and 1008 and box in box feature 102 of needle comb reticle sub-pattern 1000A will be printed along with the absence (or surrounding features) the same corresponding features of needle comb reticle sub-pattern 1000B. This would correspond to the black regions of FIG. 10. In contrast on layer n+1, the reverse would be printed, i.e., the gray or shaded regions of FIG. 10. By using complementary needle comb reticle sub-patterns 1000A, 1000B as a needle comb reticle pattern 1000, difficulties encountered with registration tools that require symmetrical marks can be overcome. Additionally, set-up time is reduced and process control measurement jobs become more robust.

[0047] The dimensions of the needle comb reticle patterns 100, 700, 1000 described above are nominal dimensions for a single embodiment for a given process size capability. Each of the dimensions enumerated above may be varied and still remain within the scope of the invention. For example, the spacing, s, between the inner box 104 and outer box frame 106 may be changed as long as the spacing, s, is sufficient to allow for registration measurements within the ordinary registration tolerance of the particular process. Another example is the width, w_(o), of the outer box frame 106 which width may be varied from about 0.5 μm to 5 μm without departing from the scope of the invention. Additionally, the needle comb reticle pattern 100, 700, 1000 of the present invention may be rotationally oriented at any angle without departing from the scope of the invention. One of ordinary skill in the art will also recognize that the dimensions outlined above may be scaled to accommodate higher or lower resolution lithographic processes as needed.

[0048] The needle comb reticle patterns 100, 700, 1000 of the present invention may be placed in any location on a semiconductor wafer or any other semiconductor substrate. However, the desire for cost effective semiconductor device fabrication dictates that active device surface area be maximized. Some portions of the perimeter of a wafer may not be large enough for a complete die pattern and a needle comb reticle pattern 100, 700, 1000 may be placed in such locations. The needle comb reticle patterns 100, 700, 1000 of the present invention are small enough to be placed on any scribe line at any location along the grid formed by the scribe lines on the wafer. Preferably, the needle comb reticle patterns 100, 700, 1000 are placed on a scribe line and adjacent to an active component region or device pattern that forms an integrated circuit die.

[0049] The number of needle comb reticle patterns 100, 700, 1000 that may be placed on a given layer is limited by the size of the scribe line. At least two needle comb reticle patterns 100, 700, 1000 must be placed on each layer in order to make CD and registration measurements. Preferably, four needle comb reticle patterns 100, 700, 1000 are placed in a rectangular field that includes a single active device pattern. Preferably, each of the four identical needle comb reticle patterns 100, 700, 1000 is placed in approximately each corner of the rectangular field. Preferably, at least one needle comb reticle pattern 100, 700, 1000 should be placed adjacent each device pattern on each layer during fabrication.

[0050] During semiconductor fabrication, a wafer may be processed using a stepper and a reticle to expose a plurality of active device patterns 804 each within a field 802 of the reticle. A field 802 is a rectangular window of a reticle. FIG. 8 is a plan view of an exemplary semiconductor wafer illustrating a field 802 of a reticle containing at least one active device pattern 804 and at least one needle comb reticle pattern 100, 700, 1000 of the present invention. Depending on the size of active device patterns 804, one or more active device patterns 804 may be placed within a field 802 of a reticle in accordance with the invention. The use of a stepper with a reticle including a field 802 is within the knowledge of one of ordinary skill in the art. Preferably, each field 802 of a reticle includes a rectangular window and four needle comb reticle patterns 100, 700, 1000, one in each corner of the field 802. A fifth needle comb reticle pattern 100, 700, 1000 may be placed in the center of the field depending on the configuration of active device patterns 804 within a field 802.

[0051]FIG. 9 is a flow chart of a method 900 of characterizing measurements from a needle comb reticle pattern to pattern critical dimension. Method 900 includes generating 902 a focus-exposure matrix, defining 904 a process window for actual pattern critical dimension and defining 906 an equivalent window for a needle comb reticle mark. Method 900 further includes determining 908 whether the needle comb reticle mark is within the equivalent window. If the needle comb reticle mark is within the equivalent window, then critical dimension will also be within the process window and there is no need to make a process control adjustment 910, i.e., the process is in control. If the needle comb reticle mark is outside the equivalent window, then there is a problem with the critical dimension measurement and the process may require adjustment 912. The above procedure may be repeated as necessary for each measurement. By characterizing measurements from a needle comb reticle pattern by method 900, the need for critical dimension measurement may be reduced or eliminated.

[0052] Although this invention has been described with reference to particular embodiments, the invention is not limited to these described embodiments. Rather, the invention is limited only by the appended claims, which include within their scope all equivalent devices or methods that operate according to the principles of the invention as described herein. 

What is claimed is:
 1. A needle comb reticle pattern for use in process measurement during semiconductor substrate processing comprising: a box-in-box feature including an inner box and an outer box frame; and two needle combs flanking said outer box frame on two adjacent sides of said outer box frame.
 2. The needle comb reticle pattern of claim 1, wherein each of said two needle combs comprises a plurality of needles emanating from a solid bar base and pointing toward said box-in-box feature.
 3. The needle comb reticle pattern of claim 2, wherein each of said plurality of needles tapers in width in stair-step fashion to a flat tip.
 4. The needle comb reticle pattern of claim 3, wherein each of said plurality of needles tapers in width from larger than stepper resolution to smaller than stepper resolution.
 5. The needle comb reticle pattern of claim 2, wherein each of said plurality of needles is approximately 1.5 μm in length.
 6. The needle comb reticle pattern of claim 2, wherein said plurality of needles are mutually spaced at a pitch of approximately 0.25 μm.
 7. The needle comb reticle pattern of claim 1, wherein said needle comb pattern is substantially square in shape with sides of approximately 22 μm in length.
 8. A semiconductor reticle used in semiconductor fabrication comprising: at least one active device pattern; and a needle comb reticle pattern adjacent to said at least one active device pattern, wherein said needle comb reticle pattern comprises: a box-in-box feature including an inner box and an outer box frame; and two needle combs flanking said outer box frame on two adjacent sides of said outer box frame.
 9. The semiconductor reticle of claim 8, wherein each of said two needle combs comprises a plurality of needles emanating from a solid bar base and pointing toward said box-in-box feature.
 10. The semiconductor reticle of claim 8, wherein each of said plurality of needles tapers in width in stair-step fashion to a flat tip.
 11. The needle comb reticle pattern of claim 9, wherein each of said plurality of needles tapers in width from larger than stepper resolution to smaller than stepper resolution.
 12. A semiconductor wafer comprising: at least one active device pattern; and at least one needle comb reticle pattern adjacent to said at least one active device pattern, wherein said at least one needle comb reticle pattern comprises: a box-in-box feature including an inner box and an outer box frame; and two needle combs flanking said outer box frame on two adjacent sides of said outer box frame.
 13. The semiconductor wafer of claim 12, wherein each of said two needle combs comprises a plurality of needles emanating from a solid bar base and pointing toward said box-in-box feature.
 14. The semiconductor wafer of claim 12, wherein each of said plurality of needles tapers in width in stair-step fashion to a flat tip.
 15. A semiconductor mask comprising: at least one active device pattern; and at least one needle comb reticle pattern adjacent to said at least one active device pattern, wherein said at least one needle comb reticle pattern comprises: a box-in-box feature including an inner box and an outer box frame; and two needle combs flanking said outer box frame on two adjacent sides of said outer box frame.
 16. The semiconductor mask of claim 15, wherein each of said two needle combs comprises a plurality of needles emanating from a solid bar base and pointing toward said box-in-box feature.
 17. The semiconductor mask of claim 16, wherein each of said plurality of needles tapers in width in stair-step fashion to a flat tip.
 18. The needle comb reticle pattern of claim 16, wherein each of said plurality of needles tapers in width from larger than stepper resolution to smaller than stepper resolution.
 19. A needle comb reticle pattern for use in process measurement during semiconductor substrate processing comprising: a box-in-box feature including an inner box and an outer box frame; two needle combs flanking said outer box frame on two adjacent sides of said outer box frame; and two reference bars flanking said outer box on two other adjacent sides of said outer box frame.
 20. The needle comb reticle pattern of claim 19, wherein each of said two needle combs comprises a plurality of needles emanating from a solid bar base and pointing toward the box-in-box feature and one of said two reference bars.
 21. The needle comb reticle pattern of claim 20, wherein each of said plurality of needles tapers in width in stair-step fashion to a flat tip.
 22. The needle comb reticle pattern of claim 21, wherein each of said plurality of needles tapers in width from larger than stepper resolution to smaller than stepper resolution.
 23. The needle comb reticle pattern of claim 20, wherein each of said plurality of needles is approximately 1.5 μm in length.
 24. The needle comb reticle pattern of claim 20, wherein said plurality of needles are mutually spaced at a pitch of approximately 0.25 μm.
 25. The needle comb reticle pattern of claim 19, wherein said needle comb pattern is substantially square in shape with sides of approximately 25 μm in length.
 26. A semiconductor reticle used in semiconductor fabrication comprising: at least one active device pattern; and a needle comb reticle pattern adjacent to said at least one active device pattern, wherein said needle comb reticle pattern comprises: a box-in-box feature including an inner box and an outer box frame; two needle combs flanking said outer box frame on two adjacent sides of said outer box frame; and two reference bars flanking said outer box on two other adjacent sides of said outer box frame.
 27. The semiconductor reticle of claim 26, wherein each of said two needle combs comprises a plurality of needles emanating from a solid bar base and pointing toward the box-in-box feature and one of said two reference bars.
 28. The semiconductor reticle of claim 27, wherein each of said plurality of needles tapers in width in stair-step fashion to a flat tip.
 29. The needle comb reticle pattern of claim 28, wherein each of said plurality of needles tapers in width from larger than stepper resolution to smaller than stepper resolution.
 30. A semiconductor wafer comprising: at least one active device pattern; and at least one needle comb reticle pattern adjacent to said at least one active device pattern, wherein said at least one needle comb reticle pattern comprises: a box-in-box feature including an inner box and an outer box frame; two needle combs flanking said outer box frame on two adjacent sides of said outer box frame; and two reference bars flanking said outer box on two other adjacent sides of said outer box frame.
 31. The semiconductor wafer of claim 30, wherein each of said two needle combs comprises a plurality of needles emanating from a solid bar base and pointing toward the box-in-box feature and one of said two reference bars.
 32. The semiconductor wafer of claim 31, wherein each of said plurality of needles tapers in width in stair-step fashion to a flat tip.
 33. A semiconductor mask comprising: at least one active device pattern; and at least one needle comb reticle pattern adjacent to said at least one active device pattern, wherein said at least one needle comb reticle pattern comprises: a box-in-box feature including an inner box and an outer box frame; two needle combs flanking said outer box frame on two adjacent sides of said outer box frame; and two reference bars flanking said outer box on two other adjacent sides of said outer box frame.
 34. The semiconductor mask of claim 33, wherein each of said two needle combs comprises a plurality of needles emanating from a solid bar base and pointing toward the box-in-box feature and one of said two reference bars.
 35. The semiconductor mask of claim 34, wherein each of said plurality of needles tapers in width in stair-step fashion to a flat tip.
 36. The needle comb reticle pattern of claim 34, wherein each of said plurality of needles tapers in width from larger than stepper resolution to smaller than stepper resolution.
 37. A method of analyzing critical dimension and registration with needle comb reticle patterns using a registration tool, said method comprising: providing a semiconductor wafer with at least one needle comb reticle pattern; providing a registration tool including: a registration tool stage; an optical registration tool; and a monitor electrically coupled to said optical registration tool; placing said semiconductor wafer on said registration tool stage; aligning said optical registration tool with said at least one needle comb reticle pattern; and analyzing critical dimension and registration from lengths measured from said at least one needle comb reticle pattern.
 38. The method of claim 37, further comprising configuring said at least one needle comb reticle pattern to include: a box-in-box feature including an inner box and an outer box frame; and two needle combs flanking said outer box frame on two adjacent sides of said outer box frame.
 39. The method of claim 38, further comprising configuring said at least one needle comb reticle pattern to include two reference bars flanking said outer box on two other adjacent sides of said outer box frame.
 40. The method of claim 37, wherein each of said two needle combs comprises a plurality of needles emanating from a solid bar base and pointing toward the box-in-box feature and one of said two reference bars.
 41. The method of claim 40, wherein each of said plurality of needles tapers in width in stair-step fashion to a flat tip.
 42. The method of claim 41, wherein each of said plurality of needles tapers in width from larger than stepper resolution to smaller than stepper resolution.
 43. The method of claim 37, further comprising repeating said aligning step and said analyzing step for each needle comb reticle pattern on said semiconductor wafer.
 44. A field of a reticle comprising: a rectangular window encompassing a plurality of active device patterns; and a plurality of needle comb reticle patterns encompassed within said rectangular window and adjacent to said plurality of active device patterns, wherein each of said plurality of needle comb reticle patterns includes: a box-in-box feature including an inner box and an outer box frame; and two needle combs flanking said outer box frame on two adjacent sides of said outer box frame.
 45. The field of a reticle of claim 44, wherein said plurality of needle comb reticle patterns comprises four needle comb reticle pattern each of which is located near a corner of said rectangular window.
 46. A field of a reticle comprising: a rectangular window encompassing a plurality of active device patterns; and a plurality of needle comb reticle patterns encompassed within said rectangular window and adjacent to said plurality of active device patterns, wherein each of said plurality of needle comb reticle patterns includes: a box-in-box feature including an inner box and an outer box frame; two needle combs flanking said outer box frame on two adjacent sides of said outer box frame; and two reference bars flanking said outer box on two other adjacent sides of said outer box frame.
 47. The field of a reticle of claim 46, wherein said plurality of needle comb reticle patterns comprises four needle comb reticle patterns each of which is located near a corner of said rectangular window.
 48. A needle comb reticle pattern for use in process measurement during semiconductor substrate processing comprising: a first needle comb reticle sub-pattern comprising: a box-in-box feature including an inner box and an outer box frame; first and second needle combs flanking said outer box frame on two opposite sides of said outer box frame having needles aligned with an axis connecting said first and second needle combs and said inner box; and third and fourth needle combs flanking said outer box frame on two other opposite sides of said outer box frame having needles aligned with an axis connecting said third and fourth needle combs and said inner box; and a second needle comb reticle sub-pattern adjacent to a single side of said first needle comb reticle sub-pattern having substantially identically dimensioned complementary features relative to said first needle comb reticle sub-pattern.
 49. A method of characterizing measurements from a needle comb reticle pattern to pattern critical dimension comprising: generating a focus-exposure matrix; defining a process window for actual pattern critical dimension; defining an equivalent window for a needle comb reticle mark; determining whether said needle comb reticle mark is within said equivalent window; and if said needle comb reticle mark is inside said equivalent window, then critical dimension will also be within said process window indicating process is in control; and if said needle comb reticle mark is outside said equivalent window, then critical dimension will also be outside said process window indicating process needs adjustment. 